6,231 research outputs found
Resolution of puzzles from the LSND, KARMEN, and MiniBooNE experiments
This work has attempted to reconcile puzzling neutrino oscillation results
from the LSND, KARMEN and MiniBooNE experiments. We show that the LSND evidence
for oscillations, its long-standing
disagreement with the results from KARMEN, and the anomalous event excess
observed by MiniBooNE in and data could all be
explained by the existence of a heavy sterile neutrino (). All these
results are found to be consistent with each other assuming that the is
created in neutral-current interactions and decays radiatively into a
photon and a light neutrino. Assuming the is produced through mixing
with , the combined analysis of the LSND and MiniBooNe excess events
suggests that the mass is in the range from 40 to 80 MeV, the mixing
strength is , and the lifetime is
s. Surprisingly, this LSND-MiniBooNE parameters
window is found to be unconstrained by the results from the most sensitive
experiments searching for heavy neutrino. We set new limits on
for the LSND-MiniBooNE favorable mass region from the precision measurements of
the Michel spectrum by the TWIST experiment. The results obtained provide a
strong motivation for a sensitive search for the in a near future
decay or neutrino experiments, which fit well in the existing/planned
experimental programs at CERN or FNAL. The question of whether the heavy
neutrino is Dirac or Majorana particle is briefly discussed.Comment: 24 pages, 28 figures, version to appear in PR
Comment on "Correlation of the Highest-Energy Cosmic Rays with Nearby Extragalactic Objects"
We argue that the data published by the Pierre Auger Collaboration
(arXiv:0711.2256) disfavor at 99% confidence level their hypothesis that most
of the highest-energy cosmic rays are protons from nearby astrophysical
sources, either Active Galactic Nuclei or other objects with a similar spatial
distribution.Comment: 1000 words, 2 figures, scicite.st
Two-body Photodisintegration of He with Full Final State Interaction
The cross sections of the processes He()H and
He()He are calculated taking into account the full final
state interaction via the Lorentz integral transform (LIT) method. This is the
first consistent microscopic calculation beyond the three--body breakup
threshold. The results are obtained with a semirealistic central NN potential
including also the Coulomb force. The cross sections show a pronounced dipole
peak at 27 MeV which lies within the rather broad experimental band. At higher
energies, where experimental uncertainties are considerably smaller, one finds
a good agreement between theory and experiment. The calculated sum of three--
and four--body photodisintegration cross sections is also listed and is in fair
agreement with the data.Comment: 18 pages, 6 figure
Exciton correlations in coupled quantum wells and their luminescence blue shift
In this paper we present a study of an exciton system where electrons and
holes are confined in double quantum well structures. The dominating
interaction between excitons in such systems is a dipole - dipole repulsion. We
show that the tail of this interaction leads to a strong correlation between
excitons and substantially affects the behavior of the system. Making use of
qualitative arguments and estimates we develop a picture of the exciton -
exciton correlations in the whole region of temperature and concentration where
excitons exist. It appears that at low concentration degeneracy of the excitons
is accompanied with strong multi-particle correlation so that the system cannot
be considered as a gas. At high concentration the repulsion suppresses the
quantum degeneracy down to temperatures that could be much lower than in a Bose
gas with contact interaction. We calculate the blue shift of the exciton
luminescence line which is a sensitive tool to observe the exciton - exciton
correlations.Comment: 27 pages in PDF and DVI format, 8 figure
The Ethical Basis for Thinking about Combating the СOVID -19 Pandemic: Albert Schweitzer’s «Reverence for Life»
The article discusses various vectors of understanding the ethical idea of «reverence for life», proposed by the doctor, humanist, Nobel laureate Albert Schweitzer more than a hundred years ago, in the context of the current crisis situation associated with the spread of a new coronavirus infection (COVID-19), which determines the relevance the topic under consideration. The novelty of the work lies in the proof of the relevance of one of the most significant concepts in the history of ethics to the modern moral conditions of the existence of mankind. The intention of the study is to emphasize the need for not only socio-economic, professional (medical), but also a deep ethical and philosophical understanding of the current situation caused by the pandemic. The article uses a historical and proper ethical approach, as well as a hypothetical-axiological method in the aspect of proving the value of one form of life over others. The main provisions of the ethical concept of Schweitzer are analyzed, and an attempt is made to give a reasoned response to its fair criticism due to the presence of an internal contradiction in the principle of reverence associated with the bifurcation of the will to live, when one life must inevitably suppress the other in order to preserve itself. Main results: the authors come to the conclusion that the moral imperative (according to which: ethics is an unlimited responsibility for everything that lives), proposed by Schweitzer, is one of the possible (and effective) imperatives that encourage society to moral reflection and more active activity to deal with the pandemic situation already in the post-Schweitzer era. During the period of missionary and professional practice in Gabon, Dr. Schweitzer himself comprehended his concept, commensurating it with the development of human civilization in the future. Directions for further research: a deep and comprehensive analysis of the moral imperatives proposed by ethical and philosophical thought in the 20th century is planned in terms of their effectiveness and relevance in the new conditions of human existence. The critically thoughtful idea of reverence for life may be one such imperative in contemporary ethics, including environmental and biomedical ethics
The Lorentz Integral Transform (LIT) method and its applications to perturbation induced reactions
The LIT method has allowed ab initio calculations of electroweak cross
sections in light nuclear systems. This review presents a description of the
method from both a general and a more technical point of view, as well as a
summary of the results obtained by its application. The remarkable features of
the LIT approach, which make it particularly efficient in dealing with a
general reaction involving continuum states, are underlined. Emphasis is given
on the results obtained for electroweak cross sections of few--nucleon systems.
Their implications for the present understanding of microscopic nuclear
dynamics are discussed.Comment: 83 pages, 31 figures. Topical review. Corrected typo
A short review of "DGP Specteroscopy"
In this paper we provide a short review of the main results developed in
hep-th/0604086. We focus on linearised vacuum perturbations about the
self-accelerating branch of solutions in the DGP model. These are shown to
contain a ghost in the spectrum for any value of the brane tension. We also
comment on hep-th/0607099, where some counter arguments have been presented.Comment: Minor typos correcte
On graviton production in braneworld cosmology
We study braneworlds in a five dimensional bulk, where cosmological expansion
is mimicked by motion through AdS. We show that the five dimensional
graviton reduces to the four dimensional one in the late time approximation of
such braneworlds. Inserting a fixed regulator brane far from the physical
brane, we investigate quantum graviton production due to the motion of the
brane. We show that the massive Kaluza-Klein modes decouple completely from the
massless mode and they are not generated at all in the limit where the
regulator brane position goes to infinity. In the low energy limit, the
massless four dimensional graviton obeys the usual 4d equation and is therefore
also not generated in a radiation-dominated universe.Comment: 9 pages, minor changes, references correcte
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